ABSTRACT The purpose of this K01 proposal is to provide me with the necessary mentored training to become an independent investigator studying the role of cell death pathways that mediate neuronal loss in individuals with Alzheimer's disease (AD). Neuronal death is a key feature of AD and the best correlate of cognitive impairment and dementia, with neurofibrillary tangle (NFT) pathology being the next-best risk factor. It is currently unknown which mechanisms promote neuronal death in early AD or how these are linked to NFTs. Studies in postmortem AD brains have demonstrated the activation of caspase-mediated cell death pathways, as well as disruption of ubiquitin-proteasome (UPS)-mediated proteolysis. The overall objective of this proposal is to study the interplay between caspases, defective UPS-mediated tau proteostasis and NFT pathology in mediating AD neuronal loss in two nuclei of the human brainstem showing the earliest vulnerability to NFTs: the dorsal raphe nucleus (DRN) and locus ceruleus (LC). We will make use of a unique collection of well- characterized human brains across the AD stages, specifically enriched with early AD brain samples, and a human-derived neuronal culture model for follow-up studies on the mechanisms of caspase activation, tau toxicity and cell death. My central hypothesis is that neuronal dysfunction and subsequent death in AD is mediated by an imbalance between caspase-cleaved tau and defective UPS tau clearance. I will test this hypothesis by pursuing the following specific aims: (1) Determine the relationship between caspase activation, caspase-cleaved tau and neuronal death in progressive stages of AD (2) Examine the role of caspases, the UPS and the co-chaperone CHIP (C terminus of the Hsc70-interacting protein) in mediating neuronal death and NFT pathology in progressive stages of AD. (3) Determine the role of caspase activation, the ubiquitin-proteasome system and CHIP in mediating neuronal death and tau pathology to patient-derived neuronal cell culture. This proposal is significant because it will generate a precise map of the interaction between cell death mechanisms and the proteasome system in mediating early neuronal death and NFTs in AD. This proposal is innovative because interventions targeting early cell death pathways in AD will promote the development of novel biomarkers and therapeutic targets. UCSF and the Gladstone Institute are ideal environments for my proposed training as they provide outstanding research facilities, training resources and excellent mentorship readily available within our scientific community. Completion of the proposed research and career development activities will inform the development of an R01 proposal for conducting independent research on the molecular profiles of the active cell death markers in AD using proteomic analyses. Our findings could inform experimental strategies on revised models for preventing AD pathogenesis before the cognitive changes appear, thus decreasing the economic and societal burden that accompanies AD.